To ensure patient safety, a blood detector must be used when using a membrane filter for blood purification to prevent critical patient conditions caused by risks such as possible blood loss, membrane rupture of the filter, mistaking of connections or hemolysis.
Spectroscopic analyses for determining blood and biological marker substances in solution are known from the prior art. EP 0 575 712 A2 describes the spectroscopic analysis of blood on a squeezed tube in dialysis and measurement in transmission. EP 1 083 948 B1 describes the spectral measurement of waste products in dialysis liquid, whereby the measurement is performed directly in the dialysis liquid discharged during dialysis treatment. The measurement is performed by spectral photometry and the measured value obtained is multiplied by the flow volume of dialysis liquid. The measurement is performed in transmission.
U.S. Pat. No. 5,644,402 describes an optical detector for blood recognition in blood treatment appliances, in which the transmission behavior of the arrangement to be measured is measured by multiple crossing of the medium measured. U.S. Pat. No. 6,718,190 B1 discloses a transmission analysis with inclined optical axes. WO 2004/057313 describes optical measurements in a squeezed tube, whereby different light sources and sensors and non-inclined optical axes are used.
However, optical transmission measurements are not possible or are imprecise, especially in optically dense solutions. Here, the question arises how certain components in the liquid are to be determined with sufficient accuracy. It may also be necessary to recognize blood in secondary liquids so as to determine a blood leak in the blood purification unit (e.g. dialysis machine).